Authenteo can run in debug mode. Go to settings in the admin explorer to set the debug mode (you must be in advanced view). Debug mode means that debugging statements will be output to the console (in Firefox) or the window (in other browsers). Authenteo provides this top level command for debugging:

debug(message)

Also, in debug mode, errors/exceptions that occur will not be caught, so that the debugged properly if you are using a Microsoft debugger (catching errors prevents the debugger from pinpointing stack traces).  In non-debug mode all errors/exceptions will be caught and displayed as an alert, so you may throw errors to display meaningful messages to users.